In recent years, along with change of design of window glasses for automobiles, ones having various shapes and curvatures are demanded. For example, in a case of rear glass, a curved glass having a complexly curved shape or a deeply curved shape having a vertical cross section of substantially J shape or S shape having a larger deformation amount that is concentrated on a partial region of the glass, is demanded.
Heretofore, as a bending method for this type of glass sheet, a bending method for a glass sheet and an apparatus therefore are proposed, wherein a heated and softened glass sheet is preliminary formed, and the preliminary formed glass sheet is subjected to a main forming to form the glass sheet into a final bent shape (for example, Patent Document 1).
The bending method and apparatus for a glass sheet of Patent Document 1 will be described with reference to FIG. 14. FIG. 14 is a view for explaining the construction of an apparatus for carrying out a conventional bending method for a glass sheet.
This apparatus has a flat mold 35′, a preliminary forming supporting frame 64′ (it is also referred to as preliminary forming ring), a preliminary forming mold 72′, a main forming supporting frame 84′ (it is also referred to as main forming ring) and a main forming mold 88′, etc.
The flat mold 35′ sucks and holds a heated and softened glass sheet G, moves the glass sheet G to a predetermined position and releases the suction-holding. By this operation, the heated and softened glass sheet G is transferred onto a preliminary forming supporting frame 64′ located at the predetermined position.
Next, the preliminary forming supporting frame 64′ on which the glass sheet G is placed, moves to a position right under the preliminary forming mold 72′.
Next, the glass sheet G placed on the preliminary forming supporting frame 64′ is preliminarily formed (press-formed) by the preliminary forming mold 72′ movable downwardly by an elevating mechanism (not shown). Namely, the glass sheet G is formed into a more gently curved shape (20 to 80% of the deformation amount from a flat-shaped glass sheet into a final shape) than a final bent shape.
Next, the preliminary formed glass sheet is placed on the main forming supporting frame 84′. The main forming supporting frame 84′ on which the glass sheet is placed moves to a position right under the main forming mold 88′.
Next, the glass sheet G placed on the main forming supporting frame 84′ is pressed against the main forming mold 88′ movable downwardly by an elevating mechanism (not shown) thereby to form the glass sheet G into a final bent shape (main forming).
As described above, by the bending method for a glass sheet described in Patent Document 1, since a preliminary bending is carried out by using a preliminary forming supporting frame and a preliminary forming mold in advance to a main forming, it is possible to realize production of a glass sheet G having an optically high quality, that has been difficult to produce by conventional technique, and having a complexly and deeply curved shape, with high productivity.    Patent Document 1: JP-A-2005-206458